Understanding tropical cirrus by combining laboratory cloud simulation and field experiments with process and circulation modelling

• Applicants: Dr. Martina Krämer; Dr. Ottmar Möhler; Professor Dr. Aiko Voigt
• Subject Area: Atmospheric Science
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392369854

This project (TropiC) is part of the PIRE International Partnership for Cirrus Studies lead by the University of Chicago. The PIRE project brings together an international team of four US American and four European expert teams for coordinated studies to advance knowledge of thin, high-altitude cirrus clouds in the cold tropical transition layer (TTL), one of the least understood region in the atmosphere. Though optically thin and often not visible, these cold ice clouds play important roles in the atmosphere and the climate system. The PIRE project focuses on formation processes of cirrus clouds, their internal dynamics, as well as their interaction with atmospheric radiative and dynamic processes. The objectives of TropiC as part of PIRE are to study and better understand (1) the process details and roles of heterogeneous and homogeneous ice formation as a source for cirrus ice crystals, (2) the equilibrium and kinetic isotopic fractionation effects of water in mixed-phase and cirrus clouds, (3) the abundance patterns of ice crystals in cirrus layers, and (4) the representation and impact of tropical cirrus clouds in global and regional model setups.TropiC is a coordinated effort of laboratory, field and modelling activities of the Karlsruhe Institute of Technology (KIT) and the Forschungszentrum Jülich (FZJ). The work program includes well-controlled cloud simulation experiments in the AIDA cloud chamber facilities at KIT, the detailed analysis of cirrus in situ measurements during StratoClim and other field activities of FZJ, and modelling studies with the process models MAID (FZJ) and ACPIM (University of Manchester), the large-scale Lagrangian type model CLaMS-Ice (FZJ), the global model framework ICON GCM (KIT), as well as the observational and process models from the PIRE consortium partners in Europe and the U.S. Among the project deliverables are new model parameterizations of cirrus processes for cloud, weather and climate models, well characterized data sets of typical cirrus cases from observations during StratoClim and AIDA cloud experiments to be used by the PIRE modelling partners as a test bed for comparing different ice nucleation and cirrus formation schemes in models, and a set of global and regional ICON simulations of the present-day climate and of global warming for comparison with the high-resolution and large-scale modeling done within the PIRE consortium. Finally, the work within this project and the whole PIRE collaboration will lead to a well advanced process understanding of TTL cirrus formation, and an extended description of cirrus clouds in the most advanced atmospheric models. Therefore, regional and global models will more accurately simulate the occurrence of TTL cirrus and their role in a changing climate. As a service to the PIRE project, new PhD students and postdocs will be trained at the unique AIDA cloud chamber facility in experimental cloud process studies and related modelling.

• DFG Programme: Research Grants
• International Connection: France, Switzerland, United Kingdom, USA
• Co-Investigators: Dr. Jens-Uwe Grooß; Privatdozent Dr. Rolf Müller; Dr. Harald Saathoff
• Cooperation Partners: Professor Dr. Thomas Ackermann; Professor Dr. Peter Blossey; Professor Dr. Paul Connolly; Professor Dr. Stephan Fueglistaler; Professor Dr. Zhiming Kuang; Professor Dr. Bernard Legras; Professorin Dr. Elizabeth J. Moyer; Professorin Dr. Tiffany A. Shaw; Professor Dr. Heini Wernli